Explosively generating electric pulses



g- 9 1970 H. E. STUBBS ET AL 3,522,459

EXPLOSIVELY GENERATING ELECTRIC PULSES Original Filed Aug. 25, 1965 United States Patent 3,522,459 EXPLOSIVELY GENERATING ELECTRIC PULSES Harry E. Stubbs and Timothy Fohl, Lexington, Mass., assiguors, by mesne assignments, to Harry Eugene Stubbs, Lexington, Mass. Continuation of application Ser. No. 482,572, Aug. 25, 1965. This application Aug. 9, 1968, Ser. No. 757,196

Int. Cl. H02k US. Cl. 310-10 10 Claims ABSTRACT OF THE DISCLOSURE Electrical pulses are generated by exploding an explosive element annular in cross-section to compress axially extending lines of magnetic force inwardly in a primarily radial direction to produce current in an output circuit element coaxial with the explosive element, preferably in the same circuit with neither a field-forming nor a conductive liner. A metal liner, annular in cross-section and coaxial with the explosive and output elements, is preferably used therebetween.

This invention relates to generating electric pulses of short duration and high power. More particularly, it provides for generating such pulses by detonation of explosives.

This application is a continuation of our application Ser. No. 482,572, now abandoned, Explosively Generating Electric Pulses, filed Aug. 25 1965.

A primary object of the invention is to provide an im proved new approach to explosive generation of elecrtic pulses of short duration with high power and other parameters. Further objects are to make possible generation of such electric pulses with equipment that is small, portable, inexpensive, and useful away from a source of electric power.

Generally speaking, the invention provides for detonating explosive annular in cross-section to drive axially extending lines of magnetic force in a primarily radial direction inwardly through a pulse output element coaxial with the explosive and constituting at least a fraction of a coil or its equivalent. In preferred embodiments, an electrically conductive liner surrounded by the explosive aids in first compressing (so that over half the lines of force driven through the coil are so driven after the lines of force density--i.e., gaussis at least five times the initial average within the liner), and then driving lines of magnetic force imposed by a permanent magnet through a central, conductive coil with a multiplicity of windings.

Other objects, features, and advantages will appear from the following description of the presently preferred embodiment taken in conjunction with the attached drawing showing a cross-sectional view thereof.

Cemented aroundcopper tube 10 long, 3' OD, 0.05" wall thickness) with acetate base cement (the cement marketed as Du Pont Adhesive No. 4684) is tubular shell 12 formed from a flexible sheet of pentaerythritol tetranitrate base explosive (marketed as Du Pont Deta Sheet C, 0.08" in thickness, and described in US. Pat. No. 2,992,087). Line generator 14 is formed in the generally conical shape shown from a thinner triangular sheet of the same material and similarly cemented to liner 10, with its edge away from its apex abutting against an edge of explosive shell 12 (suitable line generators are described in Du Pont Bulletin No. ES-58-2A). Number 8 blasting cap 16 is mounted against the apex of line generator 14. Wooden disk end support 18 carries in an axial hole wooden dowel coil form 20, on which is wrapped output coil 22, comprising a multiplicity of turns of A" copper strip. Coil 22 ends in terminals 24 and 26 (the entire output circuit, which includes said coil and terminals has a resistance of 0.0008 ohm, half of which is said coil). Permanent magnet 28 (field strength 500 gauss) is oriented to provide magnetic lines of force generally parallel to the axis of liner 10, and includes holes for accepting output cables 30.

In operation, initiating blasting cap 16 detonates explosive line generator 14, which produces a wave arriving simultaneously all around the circumference of explosive shell 12, through which the wave then proceeds as a moving ring. The liner 10 is forced to collapse radially inwardly, driving before it the field of the magnet 28, first compressing it, and then forcing it through the coil 22, to induce an EMF of 20 volts, producing a 250 kilowatt pulse of electrical power through cables 30, or over 25,000 amperes, and of about ten microseconds duration. More than half the lines of force driven through the coil 22 are at the time driven at a density more than five times the initial average density within the liner 10.

Other embodiments within the invention and the appended claims will occur to those skilled in the art. For example the output coil may be a single turn of an electrically conductive gas, or the magnet may be an electromagnet, or the liner may be omitted, or the parts disclosed may be enclosed to amplify explosive power, or a multiplicity of detonators around an end of the explosive shell may replace the explosive line generator. The invention is useful whenever pulses of short duration and high power are needed, as in magnetic pulse forming of metals.

The symmetrical quality of devices of the invention, with the output element coaxial with an explosive element |both symmetrical about the same axis and primarily radially inward compression of the field, produces greatly increased pulse-generating efficiencies. So too does use of an output circuit containing in it neither a conductive liner nor provision for creation of the lines of force to be compressed, which permits use of impedances geared to output parameters alone, and facilitates symmetry of design.

What is claimed is:

1. A pulse generator comprising an explosive element annular in cross-section, an output circuit element inside said explosive element and coaxial therewith, and a source of axially extending lines of force therebetween, whereby when said explosive element is exploded, said lines of force are driven progressively inwardly to provide primarily radial compression of said lines of force to induce a current in said output element.

2. The generator of claim 1 in which said output circuit element is in a different circuit from an electromagnet for producing said lines of force and a conductive liner interposed between said explosive element and said lines of force.

3. The generator of claim 2 in which said conductive liner is annular in cross-section and coaxial with said explosive element.

4. The generator of claim 3 in which said liner is metallic.

5. The pulse generator of claim 3 in which the distances between the parts are so related that when said explosive element is exploded to drive said liner inwardly to first compress said lines of force and then drive them through said output element, at least half the lines of force driven through said output element are so driven at a time when their density is at least five times the average initial density thereof within said conductive element.

6. The pulse generator of claim 4 in which said output element is a metallic coil.

7. The pulse generator of claim 6 in which said coil includes a multiplicity of turns.

8. A pulse generator comprising:

a cylindrical liner,

4 a coaxial annular shell of explosive therearound, tween said coil and said liner, and a line generator a line generator carried 011 said liner therearound with with an edge abutting an edge of said shell of exploan edge abutting an edge of said shell, sive. an output coil of metal with a multiplicity of turns and References Cited fiolaxiainzlvith said liner, said coil being inside said 5 UNITED STATES PATENTS a magnet mounted to provide lines of force extending 552 12/1963 cfmnon et a1 in general parallelism with said axis between said coil 12/1965 Blehl 310 11 and said linen 3,295,412 1/1967 Morley et a1. 89-8 3,356,869 12/1967 Hilton et al. 31010 9. The generator of claim 8 in which said magnet is 10 permanent. OTHER REFERENCES A.pulse generate? cqmpnsmgz Production of Very High Magnetic Fields by Imploan axially symmetric liner of electrically conductive Sion Fowlgr et 31 September 1959 pp 588 593 material, a coaxial annular shell of explosive around said liner, 15 DONOVAN R DUGGAN Primary Examiner an output coil of metal coaxial with said liner, said coil being inside said liner, US. Cl. X.R. a magnet mounted to provide magnetic lines of force 89-8 extending in general parallelism with said axis be- 

